1. Field of the Invention
Fast setting adhesive formulations in an easy applicator form are desirable for office, school and home consumers. The present invention provides a polyvinylpyrrolidone (hereinafter "PVP")-based composition in solid form, e.g. glue stick or crayon, which is easy to apply, bonds faster and is safe to use. The adhesive bonds porous substrates to which they are applied, such as paper, fabrics, polystryene foam, wood and similar porous substrate materials.
2. Description of the Related Art
U.S. Pat. Nos. 3,576,776, issued in 1971, contains a disclosure of an invention for adhesive applicator crayons comprising a shape-giving base consisting of a gel-forming salt, a liquid, and an adhesive component. Among the adhesives are listed salts of various acids, amides, and N-alkyl substituted amides including polyvinylpyrrolidone. The disclosure of U.S. Pat. No. 3,576,776 was said to be an improvement over known adhesive applicator crayons prepared from rubber, resins and waxes, which required that surface layers must be rubbed off from such crayons under relatively high pressure in order to carry out the spreading of the adhesive.
Later solid adhesive compositions, such as those disclosed in U.S. Pat. Nos. 4,073,756 and 4,075,830, were said to avoid the problem inherent in the crayons of U.S. Pat. No. 3,576,776, the long time it took to produce the adhesive composition and the high viscosity of the adhesive composition (e.g. higher than 150,000 cps) which made it difficult to fill the adhesive composition in containers.
The later patents thus used water soluble or water dispersible polymers having adhesive properties in combination with N-fatty acid acylated amino acids or salts thereof and water, or a mixture of water and one or more organic solvent(s) and/or plasticizer(s). The water dispersible or water soluble polymers having adhesive properties listed, among others, homopolymers or copolymers having a carboxyl group or a carboxylic anhydride group, where the proportions of the carboxyl and/or carboxylic anhydride group containing monomer is preferably about 30 to 100 mol %.
These, and other prior art formulations (the entire disclosures of all of which are herein incorporated by reference), were still slow to exhibit adhesive properties when dispensed, i.e. slow to exhibit paper tear when applied to bond paper.
Among other properties, the present invention provides strong final bonds and a pH generally in the range of about 8.5 to about 9.5. However, in the embodiments of the invention where a color indicator is used, the hue or intensity of the color is enhanced by having a pH more alkaline than the range given above, e.g. up to a pH of about 11, e.g. 10.9-11.1.